W. Hill Balliet

Hybridizing thermal generation, renewable energy resources, and energy storage could improve power-system affordability, reliability, resilience, and energy security. This study examines co-location and optimal sizing of baseload thermal generation like small modular reactors (SMR) with renewable generation and energy storage. Its potential is evaluated for three use cases: rural electric cooperatives and microgrids, energy-intensive manufacturing, and the bulk power system. Representative seasonal demand and generation profiles were analyzed, and the installed capacities of wind, solar, hydropower, and base-load thermal generation were optimized to minimize the battery capacity required for the combined output to follow demand. The results demonstrate that resource complementarity can reduce supply–demand mismatch and improve resource adequacy compared with standalone variable generation. For the representative rural cooperative, the optimal installed-capacity ratio was 41 parts hydro to 9.4 parts wind to 1 part thermal. For an oil refinery, the optimal configuration comprised 17 parts thermal to 6 parts hydro to 1.2 parts solar to 1 part wind. For the bulk-power-system case, represented using ISO New England data, the optimal ratio was 2.4 parts wind to 1.4 parts hydro to 1 part thermal. The findings establish the technical potential of thermal-renewable hybrids and highlight the need for future work.

Hybridizing existing hydropower plants with energy storage or other generation has the potential to improve energy security in the US and globally. However, permitting delays and direct costs to complete the regulatory process can create barriers. So far in the US, nine hydro-hybrids have received Federal Energy Regulatory Commission (FERC) approval and thirteen total hydro-hybrids have been developed. Analyzing these nine cases along with supplementary data from similar projects shows that regulatory delays have increased over the past five years. While hydro-hybrids have not yet been affected by the worst of the delays, the risk of large delays (>500 days) has increased significantly. The worst delay observed was 762 days, which effectively increased the project cost by up to 28\%. FERC could remove this barrier by reducing regulatory cost and risk with a stronger and broader categorical exclusion under the National Environmental Protection Agency and by narrowly defining FERC’s jurisdiction over hybrid assets. A broader categorical exclusion for typical hybridization projects would reduce repeated work across projects and streamline the part of the process that carries the most timeline risk. Narrowly defining FERC’s jurisdiction over secondary storage or generation assets would increase certainty about the process and streamline many projects. For example, hybridization projects that do not affect hydropower operations and already go through environmental reviews at the state or local level may not need federal regulation to ensure responsible development and operation. This would significantly reduce the cost and risk to licensees without negative environmental or social outcomes.

This paper proposes a control architecture for frequency, current, and voltage control that facilitates using battery storage to improve the response of standalone small hydropower plants. The frequency controller uses rate-of-change of frequency and frequency-Watt-based generations to produce active power commands. The distinctive feature of the controller design is that it nicely integrates response to frequency change with constraints on frequency and state of battery to enable power injections. The current and voltage control scheme allows incorporating the frequency controller. The distinctive feature of this controller is that it incorporates a bounded integral control strategy that guarantees stability. Results on the stability of the hydropower plant with proposed scheme are presented and robust ways to choose the controller gains are investigated via root locus analysis. Simulations performed show that: the hydropower plant response is significantly improved with battery storage using the proposed scheme; the load carrying capability of the hydropower plant is significantly improved with battery storage; the proposed scheme has the capability to recharge the battery; and the proposed control scheme gives improved performance.